Photoelectric device



April 3, 1956 G. E. INMAN PHOTOELECTRIC DEVICE Filed Oct. 2, 1952 g; E. lnman,

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lnven tor". Gem" WC His ATFE United States Patent PHOTGELECT RIC DEVICE George E. Inman, East Cleveland, Ohio, assignor to General Electric Company, a corporation of New Yorlr Application Dctober 2, 1952, Serial N 0. 312,7 61

7 Claims. (Cl. 201-63) This invention relates in general to photoelectric devices and more particularly to the mounting of photosensitive elements such as light sensitive crystals in sealed vitreous tubes or envelopes for obtaining improved performance and durability of such elements in use.

The present invention is of particular advantage in connection with the mounting in vitreous tubes of small crystals or semi-conductors elements of the photo-conductive type. Such crystals, in contradistinction to the photoemissive types of photoelectric devices, do not generate their own voltage but vary in impedance in accordance with the intensity of the incident radiation. In order to make use of this characteristic, it is necessary to pass a current through the crystal, the intensity of the curent or the voltage drop across the crystal then being used to control dependent apparatus. A crystal particularly suitable for this purpose is disclosed in copending application No. 190,801, filed October 16, 1950, of John E. Jacobs, entitled X-Ray Detection, and consists of a cadmium sulfide crystal substantially free from lattice distortion. These crystals, consisting of hexagonal cadmium sulfide, may be synthesized from cadmium vapor and hydrogen sulfide. Other photosensitive elements are germanium semi-conductors.

Such photo-conductive crystals are generally rather fragile and tend to be sensitive to moisture, so that in order to have a reliable and commercially practical photoelectric cell or device, it is necessary to provide a suitable mounting for them. In addition, since the crystals require the passage of a current through them in order to derive a signal for control purposes, they are liable to become overheated and thereby damaged. It will be appreciated of course that the intensity of current which may be passed through a crystal determines in general the magnitude of the signal resulting from a given variation in the incident radiation. Accordingly, increasing the heat dissipating capacity of a crystal increases in like measure its current carrying capacity and thereby its sensitivity and general utility as a photoelectric cell. Of course any mounting scheme used with such crystals must be pervious to the radiation to which the crystal is intended to be responsive, so that in general a vitreous envelope or an envelope having a vitreous window is required.

The object of the present invention is to provide new and improved mountings in the form of vitreous tubes or envelopes for photoelectric crystal elements.

Another object of the invention is to provide new and improved cell constructions for photo-conductive crystals which achieve increased sensitivity to incident radiation and a higher signal capacity.

For further objects and advantages and for a better understanding of the invention, attention is now directed to the following description and accompanying drawings.

The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

Fig. 1 is a much enlarged pictorial view of a photocell comprising a photo-conductive crystal mounted in a hermetically sealed vitreous bulb in accordance with the invention.

Fig. 2 is a side elevation of another photo-cell com prising a silvered reflector type of bulb.

Referring to Fig. l, the invention is illustrated as embodied in a photoelectric device 1, which, in its general external configuration, resembles a miniature incandescent lamp of a type in common use for automobile parking and tail lights. The device comprises a bayonet base 2 and a glass envelope 3 having a reentrant stem portion 4 sealed to the neck of the bulb at 5. The stem is formed at its upper end into a press 6 and an exhaust tube 7 projects downward through it, the juncture being made just below the press with an exhaust port 8 blown through the stem at the juncture to permit evacuation of the bulb through the exhaust tube which is tipped off at 9. A pair of support or lead-in wires 11, 12 extend through the press 6 and support a photoelectric crystal 13 at their upper ends within the bulb, their external projections being connected to the contact pins 14, 15 in the bottom insulative wall of the base.

In accordance with the illustrated embodiment of the invention, the crystal 13 is supported across the ends of the lead wires 11, 12 by shaping those ends into arcuate clamps 15 in the form of loops which are bent around the ends of the crystal. It will be appreciated that the crystals are somewhat irregular in size, no two being identical, so that the mounting means must be relatively flexible. However it is possible to grind the ends of the crystals into blunt generally wedge-shaped points 16 which facilitates mechanical support of the crystal by the clamps 15. In order to provide additional support, the lead wires 11, 12 may be sprung inwardly before mounting the crystals into the clamps so that, after the crystal is mounted, a slight spring tension is exerted upon it which serves to maintain the pointed ends 16 Within the clamp 15. Finally, the joints are coated or painted with a suitable conductive clamping paste, for instance alkadag consisting of a colloidal suspension of graphite in alcohol. The paste coating is shown on the left hand side of the crystal only, at 17.

In making the photoelectric device 1, after the crystal 13 has been mounted, the stem 4 is scaled to the bulb 3 and the envelope is then exhausted, preferably with heating to a temperature in the range of 200 to 400 C. in order to remove occluded gases from its interior. According to another feature of the invention, the bulb may then be filled with a gas of high thermal conductivity, that is a gas of low atomic weight such as hydrogen, but preferably an inert gas of these characteristics such as helium. Helium has almost ten times the heat conductivity of the more common filling gas argon and about six times that of air. The filling pressure of the helium may be approximately 600 millimeters to permit atmospheric tipping of the exhaust tube 7. The provision of this gas within the bulb provides a very decided improvement over the simple mounting of a photoconductive crystal on lead wires exposed in air, and permits a considerable increase in the allowable current through the crystal Without destructive overheating.

Referring to Fig. 2, there is shown another embodiment of our invention designed to provide greatly increased sensitivity of the photo-conductive element to radiation from a particular direction. The photoelectric device 21 comprises a vitreous envelope having a silvered portion 22 of generally parabolic form and a clear convex face 23. The parabolic portion 22 may be silvered either on the inside or the outside. The crystal 13 is mounted, as in the embodiment of Fig. l, on lead wires projecting from a stem 4 and is located substantially at the focal point of the parabolic section 22. In order to increase the heat dissipating capacity and hence the signal rating of the device, the bulb is filled with a gas of high thermal conductivity, preferably helium. Sensitivity tests have shown an improvement in sensitivity of approximately six times in the device of Fig. 2 over that of Fig. 1 for the same candle-power directed along the axis of the bulb.

The mounting arrangement for photo-conductive elements in accordance with the invention by totally enclosing the elements in sealed vitreous bulbs provides very complete protection for them in use. it also assures easy replaceability of the photoelectric devices and permits their use with standard sockets. The provision within the bulb of a cooling gas of high thermal conductivity increases the signal capacity of the crystal by an appreciable factor, and the use of a reflector type bulb with the crystal mounted at the focal point thereof achieves very high sensitivity along a selected direction.

While certain specific embodiments of the invention have been shown and described, it will of course be understood that various modifications may be made without departing from the invention. The appended claims are therefore intended to cover any such modifications coming within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead wires sealed into said bulb, a photo-conductive crystal supported within said bulb on the ends of said lead-in wires, the ends of said wires being formed into arcuate clamps receiving the ends of said crystal, said lead Wires being stressed to spring inwardly toward each other to assist in maintaining the ends of the crystal within the clamps.

2. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead Wires sealed into said bulb, a photo-conductive crystal supported within said bulb on the ends of said lead-in wires, the lead wires being stressed to spring inwardly toward each other to assist in maintaining the crystal in place on the ends thereof, and a cooling gas of high thermal conductivity from the class consisting of hydrogen and helium, within said bulb.

3. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead wires sealed into said bulb, a photo-conductive crystal element supported within said bulb on the ends of said lead-in wires, the ends of said wires being formed into arcuate clamps receiving the ends of said crystal, said lead Wires being stressed to spring inwardly toward each other to assist in maintaining the ends of the crystal within the clamps, and a cooling gas of high thermal conductivity from the class consisting of hydrogen and helium, within said bulb.

4. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead wires sealed into said bulb and having its inwardly projecting ends formed into generally arcuate clamps, a photo-conductive crystal element having its ends formed into blunt points and secured into said clamps for receiving mechanical support from said lead wires, said lead wires being stressed to spring inwardly toward each other to assist in maintaining the ends of the crystal within the clamps, and a conductive paste overlying said crystal ends to provide low resistance connections to said lead wires.

5. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead wires sealed into said bulb and having its inwardly projecting ends formed into generally arcuate clamps, a photo-conductive crystal element having its ends formed into blunt points and secured into said clamps for receiving mechanical support from said lead Wires, said lead wires being stressed to spring inwardly toward each other to assist in maintaining the ends of the crystal within the clamps, a conductive paste overlying said crystal ends to provide low resistance connections to said lead wires, and a filling of a cooling gas of high thermal conductivity from the class consisting of hydrogen and helium within said bulb.

6. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead-in wires sealed into said bulb, a base fastened to said bulb and having terminals connected to said lead wires, a cadmium sulfide crystal supported within said bulb on the ends of said lead wires, the ends of said lead wires being formed into arcuate clamps and the ends of said crystal being shaped into blunt points and entered into the openings of said clamps for receiving mechanical support therefrom, a conductive paste overlying said crystal ends to provide low resistance connections to said lead wires, and a filling of a cooling gas of high thermal conductivity from the class consisting of hydrogen and helium within said bulb for increasing the heat dissipating capacity of said crystal.

7. A photoelectric device comprising a hermetically sealed vitreous bulb, a pair of lead-in wires sealed into said bulb and a base fastened thereto and having terminals connected to the outward projections of said lead wires, a cadmium sulfide crystal supported within said bulb on the ends of said lead wires, said bulb having a concave portion with a reflective coating thereon and said crystal being located substantially at the focal point thereof, the ends of said lead wires being formed into arcuate clamps and the ends of said crystal being shaped into blunt points and entered into the openings of said clamps for receiving mechanical support therefrom, a conductive paste overlying said crystal ends to provide low resistance connections to said lead wires, and a filling of a cooling gas of high thermal conductivity from the class consisting of hydrogen and helium within said bulb for increasing the heat dissipating capacity of said crystal.

References Cited in the file of this patent UNITED STATES PATENTS 1,289,369 Berglund Dec. 31, 1918 1,702,062 Sonkin Feb. 12, 1929 2,448,518 Cashman Sept. 7, 1948 2,582,850 Rose Ian. 15, 1952 FOREIGN PATENTS 567,523 Germany Dec. 15, 1932 

1. A PHOTOELECTRIC DEVICE COMPRISING A HERMETICALLY SEALED VITREOUS BULB, A PAIR OF LEAD WIRES SEALED INTO SAID BULD, A PHOTO-CONDUCTIVE CRYSTAL SUPPORTED WITHIN SAID BULB ON THE ENDS OF SAID LEAD-IN WIRES, THE ENDS OF SAID WIRES BEING FORMED INTO ARCUATE CLAMPS RECEIVING THE ENDS OF SAID CRYSTAL, SAID LEAD WIRES BEING STRESSED TO SPRING INWARDLY TOWARD EACH OTHER TO ASSIST IN MAINTAINING THE ENDS OF THE CRYSTAL WITHIN THE CLAMPS. 